Regulations require that an aircraft is able to perform a rejected take-off and stop before the end of the runway at any time before the decision speed (V1) for that aircraft is reached (V1 is the speed above which the take-off will continue even if an engine fails or another problem occurs). Elevated brake temperatures can decrease braking performance, thereby compromising the stop distance required leading to a potential runway overrun in case of a rejected take-off which is unacceptable. To manage this risk aircraft are prevented from dispatch and take-off unless actual brake temperatures are below a threshold which ensures braking performance is met in case of a rejected take-off.
Currently, the temperature of each brake pack on an aircraft is typically monitored using thermocouples placed in the brake torque tube. Several challenges exist in measuring brake temperatures using thermocouples. The brake design and operation (e.g. movement due to wear), and the operation and installation constraints of the thermocouples limit how robust the installation can be and how close to the hottest brake discs it is possible to place a thermocouple. For a robust installation of a thermocouple into the brake equipment, the most commonly used method is to install the thermocouple in the torque tube. However; this creates an air gap between the thermocouple and the brake discs. This air gap leads to thermal lag in the readings, and moreover the thermocouples may not be able to provide useable data until after a significant cooling period has elapsed. Additionally, the correlation between the thermocouple readings and the actual brake temperatures can vary depending on the brake design. These factors mean that significant safety margins are built into aircraft dispatch procedures, and as a consequence many aircraft may wait longer before take-off than is actually necessary.
An improved system for measuring aircraft brake temperatures is therefore desired.